Process for the preparation of substantially pure tertiary olefines



.Patented Aug. 27, 1935 UNITED STATES PATENT OFFICE 'PROCESS FOR THE PREPARATION OF SUB- STANTIALLY PURE TERTIARY OLEFINES Richard M. Deanesly and William Engs, Berkeley, Calif., assignors to Shell Development Company, San Francisco,

of Delaware CaliL, a corporation No Drawing. Application March 18, 1935, Serial 22 Claims. ((31. 260-170) and the like, from the corresponding tertiary alcohols in general, and in-particular from hydrocarbon fluids containing tertiary olefines, such as derived by the pyrogenetic treatment of peat, coal, tars, oil shales, petroleum oils and products,

natural gas and like carbonaceous materials whether the treatment comprises distillation and/or cracking. The hydrocarbon fluid may be obtained from the products which are formed by the destructive hydrogenation of carbonaceous materials such as coal, brown coal, coal tar, petroleum and petroleum products, and other carbonaceous materials which are suitable for treatment by destructive distillation.

,For illustrative purposes only, reference will be had to the production of substantially pure gamma butylene although it is to be understood that corresponding members of the class or higher homologues of the tertiary oleflnes may be obtained in a similar fashion with slight modiflcations obvious to one skilled in the art, since it is well-known that the sensitivity of tertiary compounds of any series towards a reagent or under fixed conditions of pressure, temperature and/or catalyst, increases with the numberof carbon atoms in the molecule.

We have found that under regulated conditions gamma butylene, which is exemplary only, can be produced directly from-tertiary butyl alcohol by its thermal decomposition in the presence of water and an acid cataylst, preferably a mineral acid such as H2804, H3PO4 or the sulfonic acids of benzene and its homologues or acid salts of polybasic acids such as the alkalimetal salts of sulfuric'acid, phosphoric acid, etc., or the corresponding acid alkyl saltsof polybasic acids may be utilized as RHSO4, RH2PO4, R2HPO4, etc.,' wherein R represents an alkyl grouping and that a very good yield of substantially pure gamma butylene is obtainable.

To carry out the process we may either start with tertiary butyl alcohol and sulfuric acid diluted with water to the proper strength or else we may form the tertiary butyl alcohol necessary for the preparation of the gas in another part of the I process as hereinafter described. When using tertiary butyl alcohol either in the anhydrous state or as its mixture with water, we add this alcohol to aqueous sulfuric acid in such proportion that the acidity of the resulting mixture is not more than about 50% free H2504. We

prefer to dilute the mixture to a free acidity of from about 10% to 30% H2504. When the mixture is maintainedat a temperature of from about to C., gamma butylene is evolved. If the'concentration of acid is carried substantially beyond 50% H2504 in the mixture, upon adding heat to this, a large proportion of the hydi'ocarbons is lost through the formation of polymers of gamma butylene such as diand triisobutylene. I

The process may be also carried out in continuous, intermittent or batch fashion. In the former two cases, alcohol may be fed into the mixture, heat being supplied so as to maintain the evolution of. gas, at about the same rate at which gamma butylene is evolved. If theoperation is carried out under such conditions that the water formed by the dehydration of the alcohol and that contained in the alcohol feed is also evaporated at the same rate at which it is formed or fed into the system, the process is truly continuous and may be operated until the slight side reactions occurring cause the sulfuric acid to become contaminated to an extent impairing its usefulness. If the operation is conducted under vconditions such that more water-is formed or fed into the system than is evaporated during evolution of the gas, the sulfuric acid becomes more and more diluted. It may be reconcentrated and returned to the main reaction system. Undecomposed alcohol whose vapor accompanies the gamma butylene and water vapor in every case,

may be recovered and returned to the system.

In general, as the acid concentration becomes lower, the temperature of the mixture may be raised without danger of excessive polymerization.

The rate of decomposition to gamma butylene of the alcohol-acid mixture is dependent on the concentration of tertiary butyl alcohol in the decomposing kettle charge. The higher the concentration of tertiary butyl alcohol, the faster the rate of evolution of gamma butylene. It is thereforo'advantageous to maintain the concentration of ne butyl alcohol in the gamma butylene regeneration unit by addition of crude tertiary alcohol as fast as it is decomposed so as to maintain a desired high alcohol-acid ratio in the regeneration unit.

If we add to a mixture of one part of phosphoric acid (HaPOoand one part of water, 1.8 parts of tertiary amyl alcohol and heat the'mixture,

tertiary amylenes (unsymmetrical methylethylethylene and trimethylethylene) are evolved rapidly and in good yield.

as raw material for the preparation of gamma butylene, we may also prepare a solution of this alcohol in aqueous sulfuric acid by absorbing in the latter gamma butylene from hydrocarbon gases or liquids containing it. For this purpose we prefer to use a mixture of narrow boiling range containing substantially no hydrocarbons other than butanes and butylenes. It is lmown that while acid of 65-70% H2804 concentration readily absorbs gamma butylene, it has no action whatever on saturated hydrocarbons and absorbs alpha and beta butylenes at a very much lower rate. We have found thatthe gamma butylene, when absorbed in aqueous sulfuric acid, is converted to a large extent into tertiary butyl alcohol. We take advantage of this by conducting the absorption in such a manner that gamma butylene may enter the acid mixture in amounts up to molal equivalency of the water present. This. may be accomplished by adjusting the strength of the acid we employ so as to provide a sufflcient quantity of water for the hydration of the butylene to alcohol. In this way, starting with a mixture containing 35% by weight H2804, we have prepared a solution containing 7.2 mols. of alcohol per mol. of acid. With 60% acid, we can absorb up to 3.6 mols. of gamma butylene for each mol. of H2804. With 50% acid, we can absorb 5.4 mols. of gamma butylene. As the aqueous content of the acid employed 4 increases the number of mols. of gamma butylene suflicient extent to avoid'increase in temperature capable of reacting increases but a higher temperature and longer reaction period is required. The mixtures so prepared may be used in the process described above for the preparation of gamma butylene. During the absorption step, the heat of reaction should'be removed to a suflicient to cause polymerization or the loss of tertiary alcohol. Wherr" the mixture is diluted and heated, some of the alpha and beta butylene which has been absorbed from the hydrocarbon mixture is converted into secondary butyl alcohol and may be removed from the gas by condensation. That portion of alpha and gamma butylene which has been physically absorbed together with of the acid catalyst present during the execution of the process and at the same time contribute to the lowering of the acidity to that desirable for the evolution of tertiary oleflnes. The catalyst does not interfere with the absorption process; it may therefore be added at any stage of the process. Spent acid from the regeneration process may thus be utilized in the absorption process permitting economy of acid.

A suitable continuous method for carrying out our invention may be executed as follows:

The alcoholic acid mixture is fed into a decomposition unit which may be partially heated by steam coils or other heating means and partially heated by the vapors (alcohol and water) entering it from a stripping column into which is fed the overflow from the decomposition unit.

butane and has not been converted to alcohol,

may be removed from the acid liquor by any conventional degassing process before heating. We may prefer to arrange the operation in a continuous cycle by reconcentrating the sulfuric acid to the strength required for the absorption of gamma butylene and returning it to the absorption system. Various combinations of the continuous cycles disclosed are possible and will be evident to those skilled in the art.

While the procem for the production of gamma butylene here disclosedmay be operated with advantage as described, the rate of evolution of the gas from the acid'solution may be increased and the tendency to polymer formation reduced by the addition of certain catalysts. We have found that sulfates of bivalent elements, such as those of zinc, magnesium, cadmium or lead, are especially well suited for this purpose when added to the alcohol-acid mixture in such proportions efliciently as a catalyst. Alternatively, the metals themselves or their. oxides or-hydroxides may be advantageously employed as they form the salt The stripping column may be operated with live steam. 'The column and condenser which are in communication with the decomposition unit rectify and cool the tertiary olefine leaving the decomposition unit and/reflux alcohol back into it. The decomposition unit is thus, by the combination of rectification and stripping, maintained at the desired composition with respect to alcohol and acid most favorable for decomposition in good yield to tertiary olefine. The number and design of the structural parts will depend upon economical factors and operating details.

This case is a continuation-in-part of our application 632,792, filed September 12, 1932.

While we have'in the foregoing described in some detail the preferred embodiment of our invention and some variants thereof, it will be understood that this is only for the purpose of making the invention more clear and that the invention is not to be regarded as limited to the details of operation described, nor is it dependent upon the soundness or accuracy of the theories which we have advanced as to thereasons for the advantageous results attained. On the other hand. the invention is to be regarded as-limited only by the terms of the accompanying claims, in which it is our intention to claim all novelty inherent therein as broadly as is, possible in view of the prior art.

We claim as our invention:

1. A process for the preparation of substan-- -tially. pure tertiary olefine, comprising: heating an 50 aliphatic tertiary alcohol with an aqueous acidic compound in a molal ratio greater than 1:1 at

an elevated temperature whereby substantially pure tertiary olefine is evolved while maintaining the alcohol concentration by feeding alcohol at a rate at which tertiary olefine is formed.

2. A process for the preparation of substantially pure tertiary oleflne, comprising: heating an aliphatic tertiary alcohol with aqueous sulfuric. acid in a molal ratio greater than 1: 1 to an elevated temperature whereby substantially pure tertiary olefine is evolved while maintaining the alcohol concentration. 3. A process for the preparation of substantially pure gamma butylene, comprising: heating tertiary butyl alcohol with an aqueous acidic compound in a molal ratio greater than 1:1 to an elevated temperature whereby substantially .pure gamma butylene is evolved while maintaining the alcohol concentration.

4. A process for the preparation of substantially pure tertiary olefine, comprising: heating an aliphatic tertiary alcohol with an aqueous acidic compound to an elevated temperature-in metal which permits the evolution of oleflne in sulfuric acid whereby substantially pure tertiary oiefine is evolved, while substantially maintaining the alcohol concentration.

5; A process for the preparation of substantially pure gamma butylene comprising: heating an excess of tertiary butyl alcohol with aqueous sul-x furic acid in the presence of a sulfate of a'bivalent metal which permits the evolution of oleflne in sulfuric acid.

6. A process for the preparation of substantially pure gamma butylene comprising: heating tertiary butyl alcohol with aqueous sulfuric acid -in the presence of a sulfate of a bivalent metal pure gamma butylene, comprising: heating a mixture containing tertiary butyl. alcohol, water and sulfuric acid and having a free H2S04 content of not more than about 50% to a temperature between about C. to 85 C. at an absolute pressure of substantially one atmosphere while substantially maintaining the alcohol concentration in a. molal excess above that of the sulfuric acid. 9. A process for the preparation of substantially pure gamma butylene, comprising: heating a mixture containing tertiary butyl alcohol, water and sulfuric acid and having a free H2504 con tent of not more than about 50% to a temperature not greater than about 85 C. in the presence of a sulfate 'of a bivalent metal which permits the evolution of olefine.

10. A process for the preparation of substantially pure tertiary oleflne from its mixture with other hydrocarbons, comprising: the steps of:

contacting said hydrocarbons with aqueous sulfuric acid and subsequently liberating said tertiary olefine from said acid by the application of heat while maintaining the alcohol concentration in a molal ratio greater than 1:1 compared with the sulfuric acid.

11. A process for the preparation of substan'-- tially pure gamma butylene from its mixture with other hydrocarbons comprising the steps of: contacting said hydrocarbons with aqueous sulfuric acid and subsequently liberating said gamma butylene from said acid by the application of heat while maintaining the alcohol concentration in a molal excess above that of the sulfuric acid.

12. A process for the preparation of substantially'pure gamma butylene from its mixture with alcohol concentration in a molal ratio greater than 1:1 compared with the sulfuric acid.

- 13. A process for the preparation of substantially pure gamma butylenefrom its mixture with other hydrocarbons comprising the steps of contacting said hydrocarbons with aqueous sul- Y furic, acid of not nore than about 70%- H2S04 concentration, and subsequently liberating sin gamma butylene from said acid by the applica-' tion of heat while maintaining the alcohol c'on-' centration in a molal ratio greater than .1 1 com pared with the sulfuric acid. a

. 14. A process for the preparation of substan' jtially pure;gamma butylene from its mixture with other hydrocarbons comprising the'stepsofz contacting said hydrocarbons with aque'oiissulfuric acid of not more than about 70% K280i concentration, removing. said acid from contact with said hydrocarbons, diluting it to not more than about 50% HzS04 concentration and subsequently' liberating gamma butylene from said acid by the application of heat while maintaining the alcohol concentration in a molal ratio greater than 1:1 compared with the sulfuric acid.

15. A process for the preparation'of substantially puregamma butylene from its mixture with other hydrocarbons comprising the steps of contacting said hydrocarbons with aqueous sulfuric acid of not more than about 10% H2804 concentration, removing said acid from contact with said hydrocarbons, diluting it to not more than about 50% H2804 concentration and subsequently liberating gamma butylene from said acid byheatingto a temperature between about 2 70 C. and 85 C. while maintaining the alcohol concentration in a'molal excess above that ofthe sulfuric acid.

16. A process for the preparation ofsubstantially pure gamma butylene from its mixture with other hydrocarbons comprising the steps of:

contacting said hydrocarbons with aqueous sul-' furic acid of not more than about 70% H2804 concentration, removing said acid from contact with said hydrocarbons, diluting it to not more than about 50% H2SO4concentration and subsequentiy liberating gamma butylene from said acid by heating to a temperature-between about 70 C. and 85 C. in the presence of a sulfate of a bivalent metal which permits the evolution of olefine in sulfuric'acid.

.17. A process for the preparation of substantially pure gamma butylene comprising the steps of: heating tertiary butyl alcohol with aqueous sulfuric acid and continuously supplying tertiary butyl alcohol to the reaction chamber to. replace that decomposed at a rate at which tertiary butylene is formed so as to keep the alcohol concentration within the reaction chamber at a substantially constant value and in amolal ratio greater than 1:1 compared with the sulfuric acid.

18. In a process for the preparation of substantially pure'gamma. butylene from its mixture with other hydrocarbons; the steps of: absorbing gamma butylene in aqueous sulfuric acid of a strength less than 60% by weight until an excess of three mols butylene for each mol H2804 is present in the aqueous acid.

19. In a process for preparing a mixture of sulfuric-acid and tertiary butyl alcohol, the steps of absorbing gamma butylene in'aqueous H2804 of a strength not greaten'than 60% by weight until more-than 3 mols of butylene react with the water present for each mol H2504 present in the aqueous acid. 4

20. In the process of heating a mixture of H2804, H20 and tertiary alcohol whereby sub? stantially pure tertiary oleflne is evolved, the steps of: commencing the operation with not less than two molecules of alcohol per molecule of acid in the acid mixture and supplying tertiary alcohol to the reaction chamber at a rate at which tertiary oleflne is formed.

:5 less than two molecules of alcohol per molecule 0!- acid. in the acid mixture and maintaining the alcohol concentration in the acid mixture above this minimum.

22. A process for the preparation of substanpuretertiary olefine from its mixture with other hydrocarbons, comprising the steps. 01;;

contacting said hydocarbons wlthagueous 3:80,!S

in the, presence of a sulfate of a bivalent metal which permits the evolution, of oleflne in-sulfuric acid. and subsequently. liberating said tortiary olefine from said acid by the appliewxlouv of heat. 1

RICHARD M. DEANE'SLIF. v WILLIAM ENGS. 

